Fluorochemical additives have demonstrated the unique ability to modify the surface properties of polymers by adsorption at the polymer/air interface even when used at very low levels. Fluorochemicals can inherently retain these unique migrating properties while maintaining the high molecular weight necessary to minimize volatility.
The UV-absorbers of the o-hydroxyphenyl-2H-benzotriazole class have long been known as effective light stabilizers for organic materials and have enjoyed considerable commercial success.
The description, preparation and uses of these valuable 2-aryl-2H-benzotriazoles are further taught in U.S. Pat. Nos. 4,383,863; 4,853,471; 4,681,905; 3,004,896; 3,055,896; 3,072,585; 4,226,763; 4,278,589; 4,675,352; 3,189,615; 3,230,194; 4,127,586 and 3,074,910.
The hitherto known 2-aryl-2H-benzotriazoles of this group have in some circumstances exhibited limited compatibility in certain substrates, and excessive tendency to exude, sublime and and/or volatilize during processing of stabilized compositions into sheets, films, fibers or other pellicles when such processing must be done at elevated temperatures. Likewise such benzotriazoles may also suffer undue loss by volatilization or sublimation from thin films or coatings, especially when subjected to elevated temperatures during use.
Attempts have been made to increase compatibility and to reduce volatilization loss by modifying the structure of the benzotriazoles. In U.S. Pat. No. 3,230,194, a higher alkyl group was substituted for methyl, and the latter compound 2-(2-hydroxy-5-tert-octylphenyl)-2H-benzotriazole exhibited superior compatibility and performance in polyethylene.
In U.S. Pat. Nos. 4,283,327; 4,278,590 and 4,383,863 there is described 2-(2-hydroxy-3,5-di-tert-octylphenyl)-2H-benzotriazole which exhibits an excellent combination of compatibility with and/or solubility in numerous polymeric substrates along with superior resistance to loss from stabilized compositions during high temperature processing, in end-use applications where coatings or films of the stabilized compositions are exposed to ambient weathering and light exposures, and in photographic applications.
In U.S. Pat. No. 4,675,352 liquid benzotriazoles of low volatility are prepared by alkylation of 2-(2-hydroxy-5-methylphenyl)-2H-benzotriazoles.
The foregoing non-fluorine containing 2-aryl-2H-benzotriazoles have not had the ability to migrate to and to protect a polymer/air interface.
In Kobunshi Ronbunshu 47, (5), 361-70 (1990) data are reported on an improvement in U.V. stabilization by the incorporation of vinylic benzotriazoles as comonomers with perfluoroalkyl monomers. The resultant polymeric U.V. stabilizers are effective in polystyrene possibly due to the surface accumulation of surface-active segments.
U.S. Pat. No. 4,788,292 describes perfluoroalkyl substituted 1-H- and 2H-benzotriazoles which do not contain the 2-(2-hydroxyphenyl) moiety.
Certain perfluoroalkyl-phenolic benzotriazoles are reported in JP 72/011074; 72/015210; 72/043949 and 73/026012. These substituted benzotriazoles are prepared from fluorinated triazole precursors which makes them inherently expensive and not commercialy viable. They are suggested for the improvement in stability of the polymer matrix surrounding encapsulated liquid crystals.
The instant 2-(2-hydroxy-3-perfluoroalkylthiomethyl-5-alkylphenyl)-2H-benzotriazoles are easily prepared from commercially available 2-(2-hydroxy-5-alkylphenyl)-2H-benzotriazoles. Further, in the instant benzotriazoles the pendant perfluoroalkyl chains are connected by a flexible sulfur atom to the remainder of the molecule, thus providing a more mobile perfluoroalkyl function, with improved solubility.
The subject benzotriazoles exhibit excellent absorption characteristics in the ultraviolet range, low volatility, and the ability to migrate to and protect a polymer/air interface. Their photographic inertness is particularly useful in photographic compositions, especially in protecting color dye images against the harmful effects of ultraviolet light.